I tried to get this to work at one point, and IIRC the problem is that instead of sending the output back over the connection from afni to plugout_drive, afni just sends the output to its own stdout... which is cluttered with other information. So you have to a) pipe the output of afni, not of plugout_drive, and b) do some work to filter out the part of the afni output that you don't want. Here's the script I created when I was trying to figure out what that was:

$ cat testdrive_afni.bash
#!/bin/bash

afni -yesplugouts "$@" > >(sed 's/.*/\x1b\[31m&\x1b\[0m/') \
                       2> >(sed 's/.*/\x1b\[1;31m&\x1b\[0m/' 1>&2) &
plugout_drive -v 2> >(sed 's/.*/\x1b\[1m&\x1b\[0m/' 1>&2)

If you run this, you'll open an afni and get an interactive plugout_drive prompt. Both stderrs will be red, and afni's output streams will be bright or bold or whatever you have set up on your terminal for emphasis. You might need to add a few seconds of sleep between those two commands if the connection isn't establishing correctly.

HTH,
ijs